Magnetic disk drive improved in a reliability of data retrieve

ABSTRACT

A magnetic disk drive improved in reliability of data retrieve. This invention prevents the drive from decoding already-written old data. The failure decoding is caused by a deviation in a write operation, by a malfunction of a writing head and so on. When data in a sector is renewed, the sector&#39;s location and renewal frequency information are saved not only in the sector of the disk media but also in a temporary memory. When the magnetic disk drive is in an idle mode, those renewal information written in the sector and stored in the temporary memory, are checked. If both renewal information match, the data is regarded “not old” and the information about the sector in the temporary memory is deleted. In the deleting operation, check mark information indicating that the written data has been checked is written in the sector of the magnetic disk medium.

FIELD OF THE INVENTION

[0001] The present invention relates to record and reproduce techniqueof a magnetic disk drive, and more particularly to a technique forpreventing decoding old data.

BACKGROUND OF THE INVENTION

[0002] In general magnetic disk drives, positional information used toposition a magnetic head is written in a servo area as servo informationon a magnetic disk medium. Data information is written to areas, calledsectors, between servo information.

[0003] The magnetic head senses servo information at certain timeintervals, specifies the position of its track and/or its position in aradial direction while performing a sequence of positioning operationssuch as “following” and/or “seek”.

[0004] The magnetic head comprises a combination type magnetic head inwhich an MR head using a magnetoresitive effect in reproduction and athin film head using a thin film technique for coil production in recordare mounted on corresponding sliders, respectively.

[0005] In data renewal, the magnetic disk drive generally uses a methodof directly writing new data over old-written data without erasing theold data, which is referred to as “overwrite”.

[0006] A. When data is to be renewed, it is important to accuratelyposition the magnetic head at the center of the track. To position themagnetic head less accurately causes the respective positions of thealready written data and new data to be written to deviate from theirproper positions. In this case, a part of the old data, which is notrenewed or updated by the new data, could remain present and be possiblydecoded.

[0007] Most of positioning errors of the magnetic head which would occurdue to various causes can be eliminated by the servo control circuit.However, with vibrations at a frequency higher than a sensing cycle ofthe servo information, the prior-art positioning errors can not bereduced. Therefore, it is very difficult to completely eliminate theremaining old data.

[0008] In order to solve this problem, JP-A-6-338010 has proposed amethod of preventing old data decoding, by positioning a head at aplurality of different positions on a magnetic disk medium when data isto be decoded, and checking to see whether or not respective data to bedecoded coincide.

[0009] In this method, 1) since the head is positioned at a plurality ofdifferent positions on the magnetic disk medium and the data arecompared, the magnetic disk should be rotated at least twice and datareproduction time increases; and 2) this method is not effective for anabnormal operation and failure of the writing head.

[0010] B. With the complex magnetic head, there are the problems of anabnormal operation and a failure of the writing head. Old writing headseach comprise a ring-like magnetic core of high permeability and a coilwound around the core in which a current is caused to flow through thecoil to produce a magnetic field, which writes information to a magneticdisk medium.

[0011] The causes of malfunctions in the writing head are 1)disconnection and short-circuits in the coils/current paths throughwhich the currents flow, 2) corrosion of the writing head itself,physical/mechanical breakage of the writing head due to contact with themagnetic disk medium, and a deterioration in the performance of themagnetic core; and 3) an increase in the spacing between the writinghead and the magnetic disk medium due to the depositing of foreignsubstances on the surface of the magnetic head facing the medium. Theseevents greatly reduce the writing magnetic field, so that it isimpossible to erase the old data completely by renewing the old datawith new data or by writing new data over the old data.

[0012] In order to sense the state in which old data remains due toabnormality of the writing head, a history of data renewal in thelocation where the old data remains must be managed. To this end, itcould be considered to use, for example, a method of mounting asemiconductor memory on the magnetic disk drive to thereby leave historyinformation. According to this method, both the positioning errors onthe writing head and abnormality of the writing head are eliminated.Writing and recording information to and from the semiconductor memoryis performed at very high speeds and the processing time hardlyincreases.

[0013] JP-A-5-66999 discloses storing and managing managementinformation on a cache management table of a RAM.

[0014] When data renewal information in all the sectors are to be storedin a semiconductor memory, however, the capacity of the semiconductormemory needs to increase, which runs counter to cost reduction. Since acapacity of the semiconductor memory necessary to store the data renewalinformation is about 1/1000 of the whole data quantity and if it isconsidered that the cost of the semiconductor memory is several hundredstimes high per unit storage capacity compared to the cost of themagnetic writing medium, the cost of the whole magnetic disk drive wouldincrease about scores of percents.

SUMMARY OF THE INVENTION

[0015] According to an aspect of the present invention, there isproposed a magnetic disk drive including a temporary memory, whichcomprises the functions of adding, to data, a renewal frequency of datain a location (sector) when the data is to be written to the magneticdisk medium; storing the renewal frequency information in the temporarymemory; and checking the renewal information stored in the temporarymemory and that in the magnetic disk medium when the data is to bedecoded.

[0016] The magnetic disk drive may further comprise the function ofadding, to the data, information to determine whether or not both therenewal frequencies stored in the temporary memory and that stored inthe magnetic disk medium are the same and storing a resulting data.

[0017] The magnetic disk drive may further comprise the function ofdeleting the renewal information stored in the temporary memory when itis determined as a result of the checking that both the renewalfrequencies are the same.

[0018] The magnetic disk drive may further comprise the function ofreporting to a host device (controller) that both the renewalfrequencies do not accord or match when it is determined as a result ofthe checking that both the renewal information are not the same.

[0019] The magnetic disk drive may further comprise the function ofadding (writing) to the data in the location (sector) of concerninformation indicating that the result of the checking is correct andthe function of reproducing the information, which has been added to thedata in the location of concern, to decode the data if the data renewalfrequency information in the temporary memory has been deleted.

[0020] The magnetic disk drive may further comprise the function of, ifit is determined from the information added to the data that both therenewal information are not the same, reporting this fact to the hostdevice (controller).

[0021] The above means are used to perform the following processing.When data in a sector is to be renewed, information on the location ofthe sector of concern and the renewal frequency is stored in thetemporary memory. In an idle state in which there is no access from thehost device, the renewal information on the data added to the sector andthe renewal information stored in the temporary memory are checked. Whenboth coincide, the data is regarded as being not old and the sectorinformation on the temporary memory is deleted, which allows the size ofthe temporary memory to be limited in use. Renewal mark informationindicating that the renewal information has been checked is then addedto the data in the sector and written.

[0022] Use of the above means reduces the capacity of the temporarymemory, for example, a semiconductor memory that has stored the datarenewal information, to required minimum ones. Therefore, a magneticdisk drive is provided that does not greatly influence the manufacturingcost and prevents old data from being read out.

[0023] Other objects, features and advantages of the invention willbecome apparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a flowchart of data reading in a magnetic disk driveaccording to the present invention.

[0025]FIG. 2 is a block diagram of one example of the inventive magneticdisk drive.

[0026]FIG. 3 schematically illustrates servo and data informationwriting areas of a magnetic disk medium.

[0027]FIG. 4 schematically illustrates a data information writing areaon a track on the magnetic disk medium.

[0028]FIG. 5 illustrates one example of an appearance of a mechanism ofthe magnetic disk drive.

[0029]FIG. 6 is a flowchart of data writing in the inventive magneticdisk drive.

[0030]FIG. 7 is a flowchart of checking on renewal information in theinventive magnetic disk drive.

[0031]FIG. 8 schematically illustrates a state transition in a datasector in the inventive magnetic disk drive.

DESCRIPTION OF THE EMBODIMENTS

[0032]FIG. 2 is a block diagram of an overall magnetic disk driveaccording to the present invention. FIG. 5 is a perspective view of oneexample of the overall structure of the magnetic disk drive. Referencenumeral 102 denotes a magnetic disk medium; 801 a spindle motor; 101 amagnetic head; 103 an actuator; 802 a magnetic-head support mechanismthat includes head parts such as a head arm; and 804 a sealed housing.In FIG. 5, a cover (not shown) forming a main surface of the housing 804is removed so that the inside of the housing 804 can be visuallyrecognized.

[0033] The magnetic disk drive has a plurality of writing surfaces oneach of which servo information is written to position the magnetic head101 at a desired position. In an example of FIG. 3, a plurality ofconcentric tracks 301 are provided on a writing surface of the magneticdisk medium 102, on which respective tracks 301, data writing areas andposition information writing areas are disposed in an intermixing manneralong the periphery of the tracks. The servo information writing area302 includes, for example, an area where track numbers to identify therespective tracks are stored, and an area where servo information isprovided by which a positional deviation of the magnetic head 101 fromthe center of the track is to be known in the following operation of themagnetic head 101 on the track.

[0034] The magnetic disk medium 102 is rotated at a certain rotationalspeed by the spindle motor 801. Positional information that is used toposition the magnetic head 101 at a desired position is reproduced (as areproduced signal 112) by the magnetic head 101 floating while facingthe medium 102, and delivered, via the head amplifier 105, positioningcircuit 104 or data reproduce circuit 107, to the controller 109.Receiving a position control signal 111 from the positioning circuit104, the actuator 103 positions the magnetic head 101 at a targetposition on the magnetic disk medium 102 by means of the magnetic-headsupport mechanism 802. A write signal 106 from the recording circuit 108is delivered to the magnetic head 101.

[0035]FIG. 4 schematically illustrates a data writing area. Data isstored in one of sectors of a predetermined unit capacity. One or moresectors are present between servo information, each sector comprising apreamble, a synchronous part, a data part, an ECC (Error Check Code),and a postamble.

[0036] The magnetic head 101 positioned at the predetermined positiontransfers data received along with a command from the host CPU 110 tothe recording circuit 108 and the magnetic head 101 via the diskcontroller 109 and writes the data therein. When data is to be read out,the signal sensed by the reproduce head is amplified by the headamplifier 105, decoded by the data reproduce circuit 107 and thendelivered to the controller 109.

[0037] The controller 109 has a dedicated temporary memory in which datarenewal information to be delivered to a sector is stored. The temporarymemory may be provided in the controller or an external memory. Thetemporary memory is preferably a non-volatile one in order to preparefor an accidental interruption of the power supply and other possibleunexpected happenings.

[0038] A flow of data writing in this embodiment is shown in FIG. 6. Itis assumed here that the controller 109 is controlling a sequence ofoperations. A part or all of the operations may be performed by anotherelectronic circuit. The data processing comprises two steps; i.e.,writing and reading data. In an idle state in which no data processingis performed, data renewal is checked (hereinafter referred to as datachecking).

[0039] First, a data write command is given, which commands to writedata to a predetermined sector of the magnetic disk medium. Generally,serial numbers are given to the respective sectors where data are to bewritten. Assume now that an i th sector is selected.

[0040] It is then checked to see whether a renewal situation of thesector of concern has been written in the temporary memory. If so, datawill be renewed in data writing to be performed this time. Therefore,the renewal information in the temporary memory is renewed. Dataincluding this renewal information is also written to the magnetic diskmedium. If there is no information in the i th sector in the temporarymemory, an area where the data renewal situation in the i th sector isstored is retained in the memory to thereby write the renewalinformation. In addition, data including the renewal frequencyinformation is written to the disk medium.

[0041] A process for checking a sector will be described next withreference to FIG. 7. First, a sector to be checked is selected from thetemporary memory. Data is then read out from the sector. It is thenchecked to see whether the renewal situation between added one to thedata and stored one in the temporary memory accords or matches.

[0042] If so, the sector information in the temporary memory is deletedand the retained area is then opened. Then, information including checkmark information indicating that the appropriate sector is alreadychecked is written and added to the sector.

[0043] A flow of data reproduction will be described next with referenceto FIG. 1. After a read command for the i th sector information isissued, information is read out from the i th sector of the disk medium.The contents of the temporary memory are then checked and then it ischecked to see whether the information in the i th sector is present inthe temporary memory.

[0044] If so, it is then checked to see whether the renewal frequencyinformation between the data and the temporary memory accords. If so,data has normally been read out and is then transferred to the host CPU.

[0045] If not, old data has been read out and it is reported to the hostCPU that an error or old data has been read out.

[0046] In case of no sector information in the temporary memory, as aresult of the checking in connection with the data reading operation, astate in which a new sector is to be used is excluded. Therefore, thedata tried to read is considered correct, and to have been checked.

[0047] After data reading, if the information contained in the read dataincludes check mark information, the data is correct. Therefore, thedata is directly transferred to the host CPU. If the data includes nocheck mark information, it means that data could not be correctlywritten in the checking step. Therefore, this fact is then reported tothe host CPU.

[0048] In the present embodiment, the overall data area is formattedbefore the magnetic disk drive starts to be used. At this time,information that the respective sectors are already checked is added todata in the sector so that no renewal frequency information is presentin the temporary memory. After formatting, a state transition in thesector to which new data is to be written is shown in FIG. 8.

[0049] In the above example, any type of data renewal information willdo, as long as it indicates what number of times the data has beenwritten in on a certain sector. If a storage area for 3 bits isretained, it is possible to write data renewal information from the 0 thto 8 th time. The 9 th writing of such information may be returned tothe original 0 th time. Renewal information to be written to the diskmedium may be contained anywhere in the data. Alternatively, the renewalfrequency information may be converted to processing information, forexample, a polynomial expression including the renewal information, andthen written. Then, in decoding an inversely converted version of thedata may be used.

[0050] According to this invention, reading old data is preventedwithout using a large amount of temporary memory and withoutdeteriorating the writing and reading performance of the magnetic diskdrive.

[0051] Having described a preferred embodiment of the invention withreference to the accompanying drawings, it is to be understood that theinvention is not limited to the embodiments and that various changes andmodifications could be effected therein by one skilled in the artwithout departing from the spirit or scope of the invention as definedin the appended claims.

What is claimed is:
 1. A magnetic disk drive including a combinationtype magnetic head having a writing head and a reading head, a magneticdisk medium facing the combination type magnetic head, a mechanism formoving the magnetic head to a predetermined position on the magneticdisk medium, an electronic circuit having the function of reading orwriting information, and a temporary memory, the magnetic disk drivecomprising the functions of; when data is to be written to the magneticdisk medium, adding, to the data, renewal information indicating arenewal frequency of data in a writing location and writing the renewalinformation and the data; storing the renewal information in thetemporary memory; and checking the renewal information stored in thetemporary memory and in the magnetic disk medium when the data is to bedecoded.
 2. The magnetic disk drive according to claim 1, furthercomprising the function of: erasing the renewal information stored inthe temporary memory when it is determined as a result of the checkingthat both the renewal information are the same.
 3. The magnetic diskdrive according to claim 2, further comprising the function of:reporting to a host device this fact or that an error has occurred whenit is determined as a result of the checking that both the renewalinformation are not the same.
 4. The magnetic disk drive according toclaim 1, further comprising the function of: writing in the writinglocation check mark information indicating that both the renewalinformation are the same when it is determined as a result of thechecking that both the renewal information are the same.
 5. The magneticdisk drive according to claim 4, further comprising the function of:reproducing the check mark information when the data is to bereproduced.
 6. The magnetic disk drive according to claim 5, furthercomprising the function of: if it is determined from the reproducedcheck mark information that both the renewal information are not thesame, reporting to the host device this fact or that an error hasoccurred.